The present invention relates to a finned heat exchanger widely used as a condenser for an air-conditioner or a refrigeration machine.
At the time of a condensation operation of a known finned heat exchanger, refrigerant flows into two paths from inlet tubes 1 and 2 and flows out of two paths from outlet tubes 8 and 9 as shown in FIG. 11, so that an area of the flow path of the refrigerant is increased and pressure loss of the refrigerant is reduced in order to obtain higher performance.
At the time of a condensation operation of a heat exchanger, the state of refrigerant in the heat exchanger is classified into a superheated vapor range, a vapor-liquid two phase range and a subcooled liquid range. Of these ranges, the vapor-liquid two phase range in which the refrigerant has latent heat of condensation contributes most to heat exchange. Meanwhile, the subcooled liquid range is essential from a standpoint of stability of the refrigeration cycle and promotion of the refrigeration effect.
However, in the above known finned heat exchanger having two paths, since the condensation temperature of the refrigerant in the heat exchanger has dropped due to recent trends towards energy saving, a difference between the condensation temperature of the refrigerant in the heat exchanger and the temperature of air subjected to heat exchange becomes quite small, so that subcooling should be performed sufficiently. If subcooling is performed sufficiently, the subcooled liquid range which scarcely contributes to heat exchange increases greatly in the heat exchanger, thereby resulting in a drop of the capability of performing heat exchange.
In addition, if the condensation temperature is lowered and subcooling is performed sufficiently so as to improve the coefficient of performance of an air-conditioner or a refrigeration machine when the known finned heat exchanger of FIG. 11 is used as a condenser, the subcooled liquid range of the refrigerant is lower by one digit than the vapor-liquid two phase range and the difference between the condensation temperature and the temperature of air is small. Therefore, the heat transfer performance is low and the length in which the refrigerant flows in the heat transfer tube in the subcooled state becomes excessively large, thereby resulting in a large drop of the capability of the finned heat exchanger as a whole of performing heat exchange.
Meanwhile, as shown in FIGS. 12A and 12B, Japanese Patent Laid-Open Publication No. 63-183391 (1988) discloses a finned heat exchanger in which a plurality of penetrated bulge portions 14a, 14b and 14c are provided on each of opposite faces of each of elongated rectangular fins 11 in order to raise the capability of performing heat exchange. However, in this prior art finned heat exchanger, air flow resistance is large due to the penetrated bulge portions 14a to 14c of the fin 11, thus resulting in a drop of the capability of performing heat exchange.
Therefore, in order to increase the capability of performing heat exchange for an identical power of air by greatly reducing air flow resistance without unduly lowering the capability of performing heat exchange, Japanese Patent Laid-Open Publication No. 2-217792 (1990) proposes a finned heat exchanger in which a plurality of penetrated bulge portions 14a, 14b and 14c are provided on one face of each of elongated rectangular fins 11 as shown in FIGS. 13A and 13B such that a width of each of the penetrated bulge portions 14a, 14b and 14c is approximately one-third of a lateral interval between the penetrated bulge portions 14a to 14c.
Namely, heat transfer tubes 13 are, respectively, inserted into fin collars 12 obtained by burring bores arranged at a predetermined interval in a longitudinal direction of the fins 11 in each of the fins 11 as shown in FIGS. 13A and 13B, and air flows between the fins 11 in the direction of the arrow A in FIG. 13B. As shown in FIG. 13A, the fin 11 has the penetrated bulge portions arranged in three columns, i.e., two penetrated bulge portions 14b of a first column, one penetrated bulge portion 14a of a second column and three penetrated bulge portions 14c of a third column are provided between two neighboring heat transfer tubes 13. A width Wf of each of the penetrated bulge portions 14a to 14c is so set as to be approximately one-third of a lateral interval Wb between the penetrated bulge portions 14a to 14c.
Meanwhile, in the conventional finned heat exchanger of FIGS. 13A and 13B, if the heat transfer tubes 13 are arranged in a plurality of columns and there is difference in temperature between the refrigerant flowing in one heat transfer tube 13 of one of the columns and that flowing in another heat transfer tube 13 of a corresponding adjacent one of the columns, for example, the refrigerant flowing in at least one of the two neighboring heat transfer tubes 13 is in a state of subcooled liquid or superheated gas, heat exchange is performed between the refrigerants flowing in the neighboring heat transfer tubes 13 through heat conduction via a fin base having a wide flat area. Therefore, even if the heat transfer tubes are arranged in two columns in the fin 11 of FIGS. 13A and 13B, there is substantially no improvement of the capability of performing heat exchange.